1. Field of the Invention
This invention relates generally to geophysical prospecting systems and, more particularly, but not by way of limitation, to improvements in seismic prospecting methods wherein seismic information can be derived through the simultaneous operation of a plurality of vibrational seismic energy sources whereby the information produced by each source is separable from the combined recorded information.
2. Description of the Prior Art
The use of vibrational seismic energy sources is well known in the art. Present applications make use of vibrators which are controlled by a control signal whose frequency varies over a predetermined band-width of frequencies, such as a linear sweep. Subsequent correlation of the recorded seismic information with the known sweep gives an impulse equivalent seismogram. The use of the linear sweep, however, prevents the simultaneous operation of more than one vibrator or system of vibrators with the same sweep in the same geologic neighborhood, since the energy from one system will produce correlatable interference with the energy from any other operating system. It is desirable, therefore, to control each system with a distinctive continuous control signal so that the effects due to the operation of each system can be correlated out of the sum effects of all operating systems. Such a method would secure the economic benefits derived from more efficient survey operations which are obtainable with pulse sources when utilizing the pulse coding method described in "Pulse Coding in Seismic Prospecting Sosie and Seiscode" by M. G. Barbier and J. R. Viallix in the March 1974 issue of Geophysical Prospecting, Vol. 22, No. 1, pp. 153-175.